1. Field of the Invention
This invention relates to an intake system for internal combustion engines, and more particularly to an intake system for internal combustion engines in which the length of the intake system is varied or changed to enhance the output power of the engine by utilizing the inertia supercharging effect.
2. Description of the Prior Art
It has been known in the art to enhance the output power of an internal combustion engine by utilizing the inertia supercharging effect. The inertia supercharging effect is based on the synchronization of the natural frequency of the intake system with the frequency of the pressure change in the intake system caused by the reciprocating motion of the piston in the cylinder of the engine. That is, the pressure wave generated at the cylinder is transmitted through the intake passage and reflected by the surge tank and returned to the cylinder, which is repeated to make a periodical pressure change in the intake system. When the frequency of this pressure change is synchronized with the natural frequency of the intake system determined by the volume of the intake passage and the cylinder, an intake inertia effect is obtained. This is known as the inertia supercharging effect and is discussed in various prior art references such as U.S. Pat. No. 2,835,235 to Gassmann and U.K. Patent Publication No. 2,117,447. Gassmann shows that the length of the intake passage can be changed to obtain or maximize the inertia supercharging effect over a wide range of engine speeds. Further, it has been known to provide a compact arrangement to obtain the inertia supercharging effect by arranging intake passages around the surge tank as disclosed in the above U.K. patent and other printed publications such as Japanese Unexamined Patent Publication Nos. 48(1973)-58214, 56(1981)-115819 and 58(1983)-119919.
The above-mentioned prior art, however, still needs improvement in that the range of engine speeds over which the inertia supercharging effect is obtained is still small and enlargement of the range requires a complicated mechanism.
It is, therefore, desired to enlarge the range of engine speeds over which the inertia supercharging effect is obtained by use of a simple structure or mechanism.